Differential video encoding techniques are known in which new images are created with reference to previous video data. Some transmitted data may contain all of the information required for still image reconstruction, while other transmitted data may contain differential information describing changes to a reference image that has been previously decoded. The differential information is combined with the reference frames to reconstruct new images. Differential encoding may provide significant compression because it alleviates the need to transmit a complete series of still images otherwise required for moving video. As a significant disadvantage, existing video systems do not permit variable handling of reference data according to how long the reference data may usefully serve as a reference for reconstructing new images.
There remains a need for a video coding system that permits a dynamic allocation of a decoder picture memory between short-term and long-term memory.